There are currently different devices used to determine the torque applied to a part that is moveable in rotation. Said part is usually built into a mechanical system including numerous elements intended to transmit mechanical energy from the input to the output of said mechanical system.
Such devices are for example used to measure the torque applied to a transmission shaft, positioned at the engine output in a passenger vehicle. In the conventional case of a motor vehicle, these devices for example make it possible to check that the engine is transmitting power to other elements of said vehicle, such as the wheels or the alternator, in accordance with a prescribed efficiency target.
The present invention relates to a cycle transport vehicle, such as a bicycle, in which a user exerts a force on pedals linked to a crankset shaft that is rotated by said force.
In addition to checking the correct transfer of power from one end of a mechanical system to the other, such devices are also specifically required to check that the intensity of the torque applied does not exceed a given value, beyond which said torque could have a twisting effect on the shaft. For example, in the case of twisting of the crankset shaft of an electric bicycle, such a check is intended to enable the triggering of an electric motor participating in the effort required to move the bicycle, thereby contributing to the comfort of the user.
Conventionally, such an on-board device includes, in addition to a specific supporting element enabling the installation of same in said means of transport:                a shaft driven in rotation by said torque,        sensing elements able to provide a signal representing a stress applied to said at least one sensing element under the effect of said torque,        means for routing said signal to a processing module configured to determine said torque as a function of said signal.        
There are currently several types of device used to determine the torque applied to a rotating shaft. In general, they detect mechanical deformations of the shaft, for example extensions or contractions, or of certain magnitudes related to such deformations caused by said torque, using strain gauges.
Sensing elements, such as said strain gauges, are usually in direct contact with the rotating shaft, and therefore work under torsion. These latter are consequently subject to high stresses, making the implementation and use of the device not very robust.
Such layouts are also used for the routing means, on account of which it is important to take into account the phenomena of wear and periodic maintenance, in particular. More recent systems, such as differential-coupling rotary transformers, combine contactless sensing elements with contactless routing elements, but they remain equally dependent on complex electronic support, and are therefore difficult to carry on board.